Lost Circulation Compositions Comprising Pumice and Associated Methods

ABSTRACT

Disclosed are lost circulation treatment fluids and methods of sealing lost circulation zones. Embodiments include a lost circulation treatment fluid comprising pumice, hydrated lime, a set retarder, and water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent Ser. No. 14/202,625,titled “Lost Circulation Treatment Fluids Comprise Pumice and AssociatedMethods,” filed on Mar. 10, 2014, which is a continuation-in-part ofU.S. patent application Ser. No. 13/417,001, titled “Set-Delayed CementCompositions Comprising Pumice and Associated Methods,” filed on Mar. 9,2012, now U.S. Pat. No. 8,851,173, the entire disclosures of which areincorporated herein by reference.

BACKGROUND

Cement compositions may be used in a variety of subterranean operations.For example, in subterranean well construction, a pipe string (e.g.,casing, liners, expandable tubulars, etc.) may be run into a wellboreand cemented in place. The process of cementing the pipe string in placeis commonly referred to as “primary cementing.” In a typical primarycementing method, a cement composition may be pumped into an annulusbetween the walls of the wellbore and the exterior surface of the pipestring disposed therein. The cement composition may set in the annularspace, thereby forming an annular sheath of hardened, substantiallyimpermeable cement (i.e., a cement sheath) that may support and positionthe pipe string in the wellbore and may bond the exterior surface of thepipe string to the subterranean formation. Among other things, thecement sheath surrounding the pipe string functions to prevent themigration of fluids in the annulus, as well as protect the pipe stringfrom corrosion. Cement compositions also may be used in remedialcementing methods, for example, to seal cracks or holes in pipe stringsor cement sheaths, to seal highly permeable formation zones orfractures, to place a cement plug, and the like.

A broad variety of cement compositions have been used in subterraneancementing operations. In some instances, set-delayed cement compositionshave been used. Set-delayed cement compositions are characterized byremaining in a pumpable fluid state for an extended period of time(e.g., at least about 1 day to about 2 weeks or more). When desired foruse, the set-delayed cement compositions should be capable of beingactivated whereby reasonable compressive strengths are developed. Forexample, a cement set activator may be added to a set-delayed cementcomposition whereby the composition sets into a hardened mass. Amongother things, the set-delayed cement composition may be suitable for usein wellbore applications, for example, where it is desired to preparethe cement composition in advance. This may allow, for example, thecement composition to be stored prior to its use. In addition, this mayallow, for example, the cement composition to be prepared at aconvenient location and then transported to the job site. Accordingly,capital expenditures may be reduced due to a reduction in the need foron-site bulk storage and mixing equipment. This may be particularlyuseful for offshore cementing operations where space onboard the vesselsmay be limited.

Drilling requires the use of drilling fluid or as it is also known,drilling mud. One problem associated with drilling may be theundesirable loss of drilling fluid to the formation. Such lost fluidstypically may go into, for example, fractures induced by excessive mudpressures, into pre-existing open fractures, or into large openings withstructural strength in the formation. This problem may be referred to as“lost circulation,” and the sections of the formation into which thedrilling fluid may be lost may be referred to as “lost circulationzones.” In addition to drilling fluids, problems with lost circulationmay also be encountered with other treatment fluids, for example, spacerfluids, completion fluids (e.g., completion brines), fracturing fluids,and cement compositions that may be introduced into a well bore.

The loss of treatment fluids into the formation is undesirable, interalia, because of the expense associated with the treatment fluid lostinto the formation, loss of time, in extreme conditions, wellabandonment. Treatment fluid replacement does not just create operationdowntime, but may also require additional fluid storage, additionalmanpower, and additional equipment. In addition to the increasedoperating expenses, fluid replacement may create additional worksiteproblems such as higher environmental burdens and the inability torecycle fluids and materials once their respective portion of theoperation has been completed.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present method, and should not be used to limit or define themethod.

FIG. 1 illustrates a system for using a lost circulation treatment fluidwhile drilling equipment is present in a wellbore in accordance withcertain embodiments.

FIG. 2 illustrates surface equipment that may be used in the placementof a lost circulation treatment fluid into a lost circulation zone in awellbore in accordance with certain embodiments.

FIG. 3 illustrates the placement of a lost circulation treatment fluidinto a lost circulation zone in a wellbore in accordance with certainembodiments.

DETAILED DESCRIPTION

The present embodiments relate to subterranean operations and, moreparticularly, in certain embodiments, to set-delayed cement compositionsand methods of using set-delayed cement compositions in subterraneanformations. Lost circulation fluids comprising set-delayed cementcompositions may be used to prevent the loss of a variety of treatmentfluids. One of the many potential advantages to these methods andcompositions are that they may immediately plug off or bridge lostcirculation zones by developing sufficient static gel strength in ashort time frame to be effective at lost circulation control. Otheradvantages are that they may set to form a hardened mass, possesssufficient compressive strength to support well structures, may isolatesubterranean zones, and may be thixotropic (e.g., shear-thinning orshear-sensitive) so that the fluids should remain pumpable long enoughfor placement, but when static, should develop gel strength quickly.

Embodiments of the set-delayed cement compositions may generallycomprise water, pumice, hydrated lime, and a set retarder. Optionally,the set-delayed cement compositions may further comprise a dispersant.Advantageously, embodiments of the set-delayed cement compositions maybe capable of remaining in a pumpable fluid state for an extended periodof time. For example, the set-delayed cement compositions may remain ina pumpable fluid state for at least about 1 day or longer.Advantageously, the set-delayed cement compositions may developreasonable compressive strengths after activation. The set-delayedcement compositions may be suitable for a number of subterraneancementing operations, including those in subterranean formations havingbottom hole static temperatures ranging from about 100° F. to about 450°F. or even greater. In some embodiments, the set-delayed cementcomposition may be used in subterranean formations having relatively lowbottom hole static temperatures, e.g., temperatures less than about 200°F.

The water used in embodiments of the set-delayed cement compositions maybe from any source, provided that it does not contain an excess ofcompounds that may undesirably affect other components in theset-delayed cement compositions. For example, a set-delayed cementcomposition may comprise fresh water or salt water. Salt water generallymay include one or more dissolved salts therein and may be saturated orunsaturated as desired for a particular application. Seawater or brinesmay be suitable for use in certain embodiments. Further, the water maybe present in an amount sufficient to form a pumpable slurry. In certainembodiments, the water may be present in the set-delayed cementcomposition in an amount in the range of from about 33% to about 200% byweight of the pumice. In certain embodiments, the water may be presentin the set-delayed cement compositions in an amount in the range of fromabout 35% to about 70% by weight of the pumice. One of ordinary skill inthe art with the benefit of this disclosure will recognize theappropriate amount of water for a chosen application.

Embodiments of the set-delayed cement compositions may comprise pumice.Generally, pumice is a volcanic rock that may exhibit cementitiousproperties, in that it may set and harden in the presence of hydratedlime and water. The pumice may also be ground, for example. Generally,the pumice may have any particle size distribution as desired for aparticular application. In certain embodiments, the pumice may have ad50 particle size distribution in a range of from about 1 micron toabout 200 microns. The d50 particle size distribution corresponds to d50values as measured by particle size analyzers such as those manufacturedby Malvern Instruments, Worcestershire, United Kingdom. In specificembodiments, the pumice may have a d50 particle size distribution in arange of from about 1 micron to about 200 micron, from about 5 micronsto about 100 microns, or from about 10 micron to about 50 microns. Inone particular embodiment, the pumice may have a d50 particle sizedistribution of about 15 microns or less. An example of a suitablepumice is available from Hess Pumice Products, Inc., Malad, Id., asDS-325 lightweight aggregate, having a d50 particle size distribution ofabout 15 microns or less. It should be appreciated that particle sizestoo small may have mixability problems while particle sizes too largemay not be effectively suspended in the compositions. One of ordinaryskill in the art, with the benefit of this disclosure, should be able toselect a particle size for the pumice suitable for use for a chosenapplication.

Embodiments of the set-delayed cement compositions may comprise hydratedlime. As used herein, the term “hydrated lime” will be understood tomean calcium hydroxide. The hydrated lime may be included in embodimentsof the set-delayed cement compositions, for example, to form a hydrauliccomposition with the pumice. For example, the hydrated lime may beincluded in a pumice-to-hydrated-lime weight ratio of about 10:1 toabout 1:1 or 3:1 to about 5:1. Where present, the hydrated lime may beincluded in the set-delayed cement compositions in an amount in therange of from about 10% to about 100% by weight of the pumice, forexample. In some embodiments, the hydrated lime may be present in anamount ranging between any of and/or including any of about 10%, about20%, about 40%, about 60%, about 80%, or about 100% by weight of thepumice. In some embodiments, the cementitious components present in theset-delayed cement composition may consist essentially of the pumice andthe hydrated lime. For example, the cementitious components mayprimarily comprise the pumice and the hydrated lime without anyadditional components (e.g., Portland cement, fly ash, slag cement) thathydraulically set in the presence of water. One of ordinary skill in theart, with the benefit of this disclosure, will recognize the appropriateamount of the hydrated lime to include for a chosen application.

Embodiments of the set-delayed cement compositions may comprise a setretarder. A broad variety of set retarders may be suitable for use inembodiments of the set-delayed cement compositions. For example, the setretarder may comprise phosphonic acid, phosphonic acid derivatives,lignosulfonates, salts, organic acids, carboxymethylatedhydroxyethylated celluloses, synthetic co- or ter-polymers comprisingsulfonate and carboxylic acid groups, borate compounds, derivativesthereof, or mixtures thereof. Examples of suitable set retardersinclude, among others, phosphonic acid derivatives available fromHalliburton Energy Services, Houston, Tex., as Micro Matrix® cementretarder. Generally, the set retarder may be present in the set-delayedcement composition in an amount sufficient to delay the setting for adesired time. In some embodiments, the set retarder may be present inthe set-delayed cement compositions in an amount in the range of fromabout 0.01% to about 10% by weight of the pumice. In specificembodiments, the set retarder may be present in an amount rangingbetween any of and/or including any of about 0.01%, about 0.1%, about1%, about 2%, about 4%, about 6%, about 8%, or about 10% by weight ofthe pumice. One of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate amount of the set retarder toinclude for a chosen application.

As previously mentioned, embodiments of the set-delayed cementcompositions may optionally comprise a dispersant. Examples of suitabledispersants include, without limitation, sulfonated-formaldehyde-baseddispersants and polycarboxylated ether dispersants. One example of asulfonated-formaldehyde-based dispersant that may be suitable is asulfonated acetone formaldehyde condensate, available from HalliburtonEnergy Services, Houston, Tex., as CFR™-3 dispersant. One example ofpolycarboxylated ether dispersant that may be suitable is Liquiment®514L dispersant, available from BASF Corporation, Houston, Tex., thatcomprises 36% by weight of the polycarboxylated ether in water. While avariety of dispersants may be used in accordance with certainembodiments, polycarboxylated ether dispersants may be particularlysuitable for use in some embodiments. Without being limited by theory,it is believed that polycarboxylated ether dispersants maysynergistically interact with other components of the set-delayed cementcomposition. For example, it is believed that the polycarboxylated etherdispersants may react with certain set retarders (e.g., phosphonic acidderivatives) resulting in formation of a gel that suspends the pumiceand hydrated lime in the composition for an extended period of time.

In some embodiments, the dispersant may be included in the set-delayedcement compositions in an amount in the range of from about 0.01% toabout 5% by weight of the pumice. In specific embodiments, thedispersant may be present in an amount ranging between any of and/orincluding any of about 0.01%, about 0.1%, 0.5%, about 1%, about 2%,about 3%, about 4%, or about 5% by weight of the pumice. One of ordinaryskill in the art, with the benefit of this disclosure, will recognizethe appropriate amount of the dispersant to include for a chosenapplication.

Other additives suitable for use in subterranean cementing operationsalso may be included in embodiments of the set-delayed cementcompositions. Examples of such additives include, but are not limitedto, weighting agents, lightweight additives, gas-generating additives,mechanical-property-enhancing additives, lost-circulation materials,filtration-control additives, fluid-loss-control additives, defoamingagents, foaming agents, thixotropic additives, and combinations thereof.In embodiments, one or more of these additives may be added to theset-delayed cement composition after storing but prior to placement ofthe set-delayed cement composition into a subterranean formation. Aperson having ordinary skill in the art, with the benefit of thisdisclosure, will readily be able to determine the type and amount ofadditive useful for a particular application and desired result.

Optionally, foaming additives may be included in the set-delayed cementcompositions to, for example, facilitate foaming and/or stabilize theresultant foam formed therewith. In particular, the cement compositionsmay be foamed with a foaming additive and a gas. The foaming additivemay include a surfactant or combination of surfactants that reduce thesurface tension of the water. By way of example, the foaming agent maycomprise an anionic, nonionic, amphoteric (including zwitterionicsurfactants), cationic surfactant, or mixtures thereof. Examples ofsuitable foaming additives include, but are not limited to: betaines;anionic surfactants such as hydrolyzed keratin; amine oxides such asalkyl or alkene dimethyl amine oxides; cocoamidopropyl dimethylamineoxide; methyl ester sulfonates; alkyl or alkene amidobetaines such ascocoamidopropyl betaine; alpha-olefin sulfonates; quaternary surfactantssuch as trimethyltallowammonium chloride and trimethylcocoammoniumchloride; C8 to C22 alkylethoxylate sulfates; and combinations thereof.Specific examples of suitable foaming additives include, but are notlimited to: mixtures of an ammonium salt of an alkyl ether sulfate, acocoamidopropyl betaine surfactant, a cocoamidopropyl dimethylamineoxide surfactant, sodium chloride, and water; mixtures of an ammoniumsalt of an alkyl ether sulfate surfactant, a cocoamidopropylhydroxysultaine surfactant, a cocoamidopropyl dimethylamine oxidesurfactant, sodium chloride, and water; hydrolyzed keratin; mixtures ofan ethoxylated alcohol ether sulfate surfactant, an alkyl or alkeneamidopropyl betaine surfactant, and an alkyl or alkene dimethylamineoxide surfactant; aqueous solutions of an alpha-olefinic sulfonatesurfactant and a betaine surfactant; and combinations thereof. Anexample of a suitable foaming additive is ZONESEALANT™ 2000 agent,available from Halliburton Energy Services, Inc.

Optionally, strength-retrogression additives may be included in theset-delayed cement compositions to, for example, prevent theretrogression of strength after the cement composition has been allowedto develop compressive strength when the cement composition is exposedto high temperatures. These additives may allow the cement compositionsto form as intended, preventing cracks and premature failure of thecementitious composition. Examples of suitable strength-retrogressionadditives may include, but are not limited to, amorphous silica, coarsegrain crystalline silica, fine grain crystalline silica, or acombination thereof.

Optionally, lightweight additives may be included in the set-delayedcement compositions to, for example, decrease the density of the cementcompositions. Examples of suitable lightweight additives include, butare not limited to, bentonite, coal, diatomaceous earth, expandedperlite, fly ash, gilsonite, hollow microspheres, low-density elasticbeads, nitrogen, pozzolan-bentonite, sodium silicate, combinationsthereof, or other lightweight additives known in the art.

Optionally, gas-generating additives may be included in the set-delayedcement compositions to release gas at a predetermined time, which may bebeneficial to prevent gas migration from the formation through thecement composition before it hardens. The generated gas may combine withor inhibit the permeation of the cement composition by formation gas.Examples of suitable gas-generating additives include, but are notlimited to, metal particles (e.g., aluminum powder) that react with analkaline solution to generate a gas.

Optionally, mechanical-property-enhancing additives may be included inthe set-delayed cement compositions to, for example, ensure adequatecompressive strength and long-term structural integrity. Theseproperties can be affected by the strains, stresses, temperature,pressure, and impact effects from a subterranean environment. Examplesof mechanical-property-enhancing additives include, but are not limitedto, carbon fibers, glass fibers, metal fibers, mineral fibers, silicafibers, polymeric elastomers, latexes, and combinations thereof.

Optionally, lost-circulation materials may be included in theset-delayed cement compositions to, for example, help prevent the lossof fluid circulation into the subterranean formation. Examples oflost-circulation materials include but are not limited to, cedar bark,shredded cane stalks, mineral fiber, mica flakes, cellophane, calciumcarbonate, ground rubber, polymeric materials, pieces of plastic,grounded marble, wood, nut hulls, melamine laminates (e.g., Foimica®laminate), corncobs, cotton hulls, and combinations thereof.

Optionally, fluid-loss-control additives may be included in theset-delayed cement compositions to, for example, decrease the volume offluid that is lost to the subterranean formation. Properties of thecement compositions may be significantly influenced by their watercontent. The loss of fluid can subject the cement compositions todegradation or complete failure of design properties. Examples ofsuitable fluid-loss-control additives include, but not limited to,certain polymers, such as hydroxyethyl cellulose,carboxymethylhydroxyethyl cellulose, copolymers of2-acrylamido-2-methylpropanesulfonic acid and acrylamide orN,N-dimethylacrylamide, and graft copolymers comprising a backbone oflignin or lignite and pendant groups comprising at least one memberselected from the group consisting of2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile, andN,N-dimethylacrylamide.

Optionally, defoaming additives may be included in the set-delayedcement compositions to, for example, reduce tendency for the cementcomposition to foam during mixing and pumping of the cementcompositions. Examples of suitable defoaming additives include, but arenot limited to, polyol silicone compounds. Suitable defoaming additivesare available from Halliburton Energy Services, Inc., under the productname D-AIR™ defoamers.

Optionally, thixotropic additives may be included in the set-delayedcement compositions to, for example, provide a cement composition thatcan be pumpable as a thin or low viscosity fluid, but when allowed toremain quiescent attains a relatively high viscosity. Among otherthings, thixotropic additives may be used to help control free water,create rapid gelation as the slurry sets, combat lost circulation,prevent “fallback” in annular column, and minimize gas migration.Examples of suitable thixotropic additives include, but are not limitedto, gypsum, water soluble carboxyalkyl, hydroxyalkyl, mixed carboxyalkylhydroxyalkyl either of cellulose, polyvalent metal salts, zirconiumoxychloride with hydroxyethyl cellulose, or a combination thereof.

Those of ordinary skill in the art will appreciate that embodiments ofthe set-delayed cement compositions generally should have a densitysuitable for a particular application. By way of example, theset-delayed cement compositions may have a density in the range of fromabout 4 pounds per gallon (“lb/gal”) to about 20 lb/gal. In certainembodiments, the set-delayed cement compositions may have a density inthe range of from about 8 lb/gal to about 17 lb/gal. Embodiments of theset-delayed cement compositions may be foamed or unfoamed or maycomprise other means to reduce their densities, such as hollowmicrospheres, low-density elastic beads, or other density-reducingadditives known in the art. In embodiments, the density may be reducedafter storing the composition, but prior to placement in a subterraneanformation. Those of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate density for a particularapplication.

As previously mentioned, embodiments of the set-delayed cementcompositions may rapidly develop static gel strength. For example, theset-delayed cement compositions may be characterized by a static gelstrength of at least about 100 lb/100 ft² to about 500 lb/100 ft² atabout 50 to about 200° F. By way of further example, the set-delayedcement compositions may be characterized by a static gel strength of atleast about 200 lb/100 ft² to about 350 lb/100 ft² at about 50 to about200° F.

As previously mentioned, the set-delayed cement compositions may have adelayed set in that they remain in a pumpable fluid state for anextended period of time. For example, the set-delayed cementcompositions may remain in a pumpable fluid state at a temperature, forexample, about 100° F., for a period of time from about 1 day to about 7days or more. In some embodiments, the set-delayed cement compositionsmay remain in a pumpable fluid state at a temperature, for example,about 100° F., for at least about 1 day, about 7 days, about 10 days,about 20 days, about 30 days, about 40 days, about 50 days, about 60days, or longer. A fluid is considered to be in a pumpable fluid statewhere the fluid has a consistency of less than 70 Bearden units ofconsistency (“Bc”), as measured on a high-temperature high-pressureconsistometer at room temperature (e.g., about 80° F.) in accordancewith the procedure for determining cement thickening times set forth inAPI RP Practice 10B-2, Recommended Practice for Testing Well Cements,First Edition, July 2005.

When desired for use, embodiments of the set-delayed cement compositionsmay be activated (e.g., by combination with a cement set activator) tothereby set into a hardened mass. By way of example, embodiments of theset-delayed cement compositions may be activated to set to form ahardened mass in a time period in the range of from about 2 hours toabout 12 hours. For example, embodiments of the set-delayed cementcompositions may set to form a hardened mass in a time period rangingbetween any of and/or including any of about 2 hours, about 4 hours,about 6 hours, about 8 hours, about 10 hours, or about 12 hours. Afteractivation, the set-delayed cement composition may develop a 24-hourcompressive strength in the range of from about 50 psi to about 5000psi, alternatively, from about 100 psi to about 4500 psi, oralternatively from about 500 psi to about 4000 psi. In some embodiments,the set-delayed cement composition may develop a compressive strength in24 hours of at least about 50 psi, at least about 100 psi, at leastabout 500 psi, or more. The compressive strengths may be determined inaccordance with API RP 10B-2, Recommended Practice for Testing WellCements, First Edition, July 2005, using an UCA at 140° F. whilemaintained at 3000 psi.

Embodiments may include addition of a cement set activator to theset-delayed cement compositions. Examples of suitable cement setactivators include, but are not limited to, calcium chloride,triethanolamine, sodium silicate, zinc formate, calcium acetate, sodiumhydroxide, a monovalent salt, nanosilica (i.e., silica having a particlesize of less than or equal to about 100 nanometers), a polyphosphate,and combinations thereof. In some embodiments, a combination of thepolyphosphate and a monovalent salt may be used for activation. Themonovalent salt used may be any salt that dissociates to form amonovalent cation, such as sodium and potassium salts. Specific examplesof suitable monovalent salts include potassium sulfate, calciumchloride, and sodium sulfate. A variety of different polyphosphates maybe used in combination with the monovalent salt for activation of theset-delayed cement compositions, including polymeric metaphosphatesalts, phosphate salts, and combinations thereof, for example. Specificexamples of polymeric metaphosphate salts that may be used includesodium hexametaphosphate, sodium trimetaphosphate, sodiumtetrametaphosphate, sodium pentametaphosphate, sodiumheptametaphosphate, sodium octametaphosphate, and combinations thereof.A specific example of a suitable cement set activator comprises acombination of sodium sulfate and sodium hexametaphosphate. Inparticular embodiments, the activator may be provided and added to theset-delayed cement composition as a liquid additive, for example, aliquid additive comprising a monovalent salt, a polyphosphate, andoptionally a dispersant.

The cement set activator should be added to embodiments of theset-delayed cement composition in an amount sufficient to activate theextended settable composition to set into a hardened mass. In certainembodiments, the cement set activator may be added to the set-delayedcement composition in an amount in the range of about 1% to about 20% byweight of the pumice. In specific embodiments, the cement set activatormay be present in an amount ranging between any of and/or including anyof about 1%, about 5%, about 10%, about 15%, or about 20% by weight ofthe pumice. One of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate amount of the cement setactivator to include for a chosen application.

As will be appreciated by those of ordinary skill in the art,embodiments of the set-delayed cement compositions may be used in avariety of subterranean operations, including drilling, fluiddisplacement, and primary and remedial cementing. Collectively, thesetypes of operations may use the set-delayed cement composition as a“treatment fluid.” As used herein, the term “treatment,” or “treating”fluid refers to any subterranean operation that uses a fluid inconjunction with a desired function and/or for a desired purpose. Theterm “treatment,” or “treating,” does not imply any particular action bythe fluid.

In some embodiments, a set-delayed cement composition may be providedthat comprises water, pumice, hydrated lime, a set retarder, andoptionally a dispersant. The set-delayed cement composition may bestored, for example, in a vessel or other suitable container. Theset-delayed cement composition may be permitted to remain in storage fora desired time period. For example, the set-delayed cement compositionmay remain in storage for a time period of about 1 day or longer. Forexample, the set-delayed cement composition may remain in storage for atime period of about 1 day, about 2 days, about 5 days, about 7 days,about 10 days, about 20 days, about 30 days, about 40 days, about 50days, about 60 days, or longer. In some embodiments, the set-delayedcement composition may remain in storage for a time period in a range offrom about 1 day to about 7 days or longer. Thereafter, the set-delayedcement composition may be activated, for example, by addition of acement set activator, introduced into a subterranean formation, andallowed to set therein.

The set-delayed cement compositions may comprise properties that wouldbe beneficial for use as a lost circulation treatment fluid. Forexample, the lost circulation composition may develop static gelstrength in a short time frame enabling them to be effective at lostcirculation control. By way of further example, the set-delayed cementcompositions may set to form a hardened mass with sufficient compressivestrength to support well structures. Additionally, the set-delayedcement compositions may be thixotropic (e.g., shear-thinning orshear-sensitive) so that the fluids should remain pumpable long enoughfor placement, but when static, should develop gel strength quickly.

Accordingly, embodiments provide a lost circulation treatment fluid thatcomprises a set-delayed cement composition. The lost circulationtreatment fluid may be used in the course of drilling a wellbore in asubterranean formation; the lost circulation treatment fluid maycomprise a set-delayed cement composition that may comprise: water,pumice, hydrated lime, a set retarder, and optionally a dispersant. Thelost circulation treatment fluid further may comprise a cement setactivator. The lost circulation treatment fluid may be used to reducethe loss of drilling fluid into the lost circulation zones of thesubterranean formation. In further embodiments, the lost circulationtreatment fluid may be used at any time and during any wellboreoperation. The lost circulation fluid may be used to reduce the loss ofany treatment fluid to any formation feature.

The lost circulation treatment fluid may be a thixotropic shear-thinningfluid. A thixotropic fluid is generally described as a fluid thatbecomes more viscous when flow ceases. It often may develop a gel thatrequires a sufficient shear stress to overcome this static gellingphenomenon, in order for flow to begin. Once flow begins, a shearthinning or pseudoplastic fluid is one whose apparent viscosity(apparent viscosity being defined as the ratio of shear stress to shearrate) decreases as shear rate increases. Dilatant (shear thickening)fluids are those whose apparent viscosity increases as shear rateincreases. The Herschel-Bulkley (HB) fluid model can be used toviscometrically classify fluids both as shear-thinning (pseudoplastic)or shear thickening (dilatant). The HB model is expressed as:

τ=μ_(∞)γ^(n)+τ₀

Where τ is the shear stress, μ_(∞) is the consistency coefficient of thefluid, γ is the shear rate, n is the shear-thinning index, and τ₀ is theyield stress. A shear-thinning index of less than 1 indicates that thefluid is shear-thinning, whereas a value of n that is greater than 1indicates that the fluid is shear-thickening. Thus, a shear-thinningfluid must have a shear-thinning index of less than 1 when measuredaccording to the Herschel-Bulkley model. The thixotropic andshear-thinning dual nature of lost circulation treatment fluids willtherefore remain fluid while exposed to the agitation of pumping (or anyother agitation), however, when the lost-circulation treatment fluidflows into a lost circulation zone and away from a source of agitationthe lost circulation treatment fluid will thicken to seal the lostcirculation zone and prevent fluid migration into the lost circulationzone of any fluid flowing adjacent to the sealed lost circulation zone.

In lost circulation treatment fluid embodiments, a lost circulationtreatment fluid that comprises a set-delayed cement composition may beused. For example, the lost circulation treatment fluid embodimentscomprise the formulations of the disclosed set-delayed cementcomposition described herein. In embodiments, the lost circulationtreatment fluid may be comprised entirely of the set-delayed cementcomposition. Therefore, in embodiments, the disclosed set-delayed cementcomposition may be used to reduce the loss of a treatment fluid in asubterranean formation, e.g., by circulating the set-delayed cementcomposition while drilling a wellbore, the lost circulation treatmentfluid may reduce the loss of drilling fluid to the lost circulationzones of a subterranean formation. An embodiment may provide a method ofdrilling a wellbore in a subterranean formation comprising: circulatinga lost circulation treatment fluid comprising a set-delayed cementcomposition in the wellbore while drilling the wellbore, wherein theset-delayed cement composition comprises: pumice, hydrated lime, a setretarder, and water. In further embodiments, all or a portion of theset-delayed cement composition is permitted to set in the lostcirculation zones of the subterranean formation.

In optional lost circulation treatment fluid embodiments, aluminumsulfate, i.e. Al₂(SO₄)₃, may be used to enhance the rheology of the lostcirculation treatment fluid. This enhancement may be measured byapplication of the Herschel-Bulkley model described earlier, wherein theaddition of aluminum sulfate induces a net decrease in the value of theshear-thinning index. The lost circulation treatment fluid may comprisealuminum sulfate in an amount of about 0.1% to about 10% by weight ofthe pumice. In specific embodiments, the aluminum sulfate may be presentin an amount ranging between any of and/or including any of about 0.1%,about 0.5%, about 1%, about 2%, about 5%, about 7%, or about 10% byweight of the pumice. One of ordinary skill in the art, with the benefitof this disclosure, will recognize the appropriate amount of aluminumsulfate to include for a chosen application. Aluminum sulfate inducesthe formation of ettringite in the lost circulation treatment fluid.Without being limited by theory, it is believed that ettringite formsneedle like crystals whose flow properties induce thixotropy becausethey align in a shear field and become randomized when static.Therefore, in embodiments, any other material that induces the formationof ettringite may be used in a manner similar to aluminum sulfate.

As previously mentioned, lost circulation zones are often encounteredinto which drilling fluid may be lost. As a result, drilling typicallymust be terminated with the implementation of remedial procedures, forexample. In accordance with embodiments, the lost circulation treatmentfluids may be used to seal the lost circulation zones to prevent theuncontrolled flow of treatment fluids into or out of the lostcirculation zones, e.g., lost drilling fluid circulation, crossflows,underground blow-outs and the like. In an embodiment, a lost circulationtreatment fluid comprising a set-delayed cement composition mayprepared. After preparation, the lost circulation treatment fluid may beintroduced into the lost circulation zone. In an embodiment, the lostcirculation treatment fluid is pumped through one or more openings atthe end of the string of drill pipe. For example, the lost circulationtreatment fluid may be pumped through the drill bit. Once placed intothe lost circulation treatment fluid, the lost circulation treatmentfluid should set to form a hardened mass inside the lost circulationzone. This hardened mass should seal the zone and control the loss ofsubsequently pumped drilling fluid, which allows for continued drilling.In addition to drilling fluids, embodiments of the lost circulationtreatment fluids may also be used to control lost circulation problemsencountered with other treatment fluids, for example, spacer fluids,completion fluids (e.g., completion brines), fracturing fluids, andcement compositions (set-delayed or otherwise) that may be placed into awellbore.

A method of sealing a lost circulation zone may be provided. The methodmay comprise circulating a lost circulation treatment fluid in awellbore, wherein the lost circulation treatment fluid comprises pumice,hydrated lime, a set retarder, and water; and allowing the lostcirculation treatment fluid to set in the lost circulation zone to sealthe lost circulation zone. The lost circulation treatment fluid used inthis method of sealing the lost circulation may contain the variousfeatures of the embodiments of the lost circulation treatment fluiddescribed herein.

A lost circulation treatment fluid may be provided. The lost circulationtreatment fluid may comprise pumice, hydrated lime, a set retarder, andwater. The lost circulation treatment fluid may contain the variousfeatures of the embodiments of the lost circulation treatment fluiddescribed herein.

A system for sealing a lost circulation zone in a subterranean formationmay be provided. The system may comprise a lost circulation treatmentfluid for placement into the lost circulation zone. The lost circulationtreatment fluid may comprise pumice, hydrated lime, and a set retarder.The lost circulation treatment fluid may further comprise mixingequipment capable of missing the lost circulation treatment fluid; andpumping equipment capable of pumping the lost circulation treatmentfluid into the lost circulation zone.

FIG. 1 illustrates an example technique for the introduction of a lostcirculation treatment fluid 122 comprising the set-delayed cementcompositions disclosed herein into a lost circulation zone 125 whiledrilling equipment is present in a wellbore 116. Such an embodiment maybe used, for example, when it is desired to reduce the loss of drillingfluid into a lost circulation zone 125. As such, the exemplary lostcirculation treatment fluids which comprise the set-delayed cementcompositions disclosed herein may directly or indirectly affect one ormore components or pieces of equipment associated with the preparation,delivery, recapture, recycling, reuse, and/or disposal of the disclosedset-delayed cement compositions. For example, and with reference to FIG.1, the lost circulation treatment fluids 122 may directly or indirectlyaffect one or more components or pieces of equipment associated with anexemplary wellbore drilling assembly 100, according to one or moreembodiments. It should be noted that while FIG. 1 generally depicts aland-based drilling assembly, those skilled in the art will readilyrecognize that the principles described herein are equally applicable tosubsea drilling operations that employ floating or sea-based platformsand rigs, without departing from the scope of the disclosure.

As illustrated, the drilling assembly 100 may include a drillingplatform 102 that supports a derrick 104 having a traveling block 106for raising and lowering a drill string 108. The drill string 108 mayinclude, but is not limited to, drill pipe and coiled tubing, asgenerally known to those skilled in the art. A kelly 110 supports thedrill string 108 as it is lowered through a rotary table 112. A drillbit 114 is attached to the distal end of the drill string 108 and isdriven either by a downhole motor and/or via rotation of the drillstring 108 from the well surface. As the bit 114 rotates, it creates awellbore 116 that penetrates various subterranean formations 118.

A pump 120 (e.g., a mud pump) circulates lost circulation treatmentfluid 122 through a feed pipe 124 and to the kelly 110, which conveysthe lost circulation treatment fluid 122 downhole through the interiorof the drill string 108 and through one or more orifices in the drillbit 114. The lost circulation treatment fluid 122 may be introducedprior to, concurrently with, or subsequent to the introduction of adrilling fluid or other treatment fluid (not shown) into the wellbore.The lost circulation treatment fluid 122 may then contact lostcirculation zone 125. The lost circulation treatment fluid 122 thatcontacts lost circulation zone 125 may no longer be exposed tosufficient shear force to remain fluid and once static, lost circulationtreatment fluid 122 may thicken to seal lost circulation zone 125 andeventually set to form a hardened mass. The lost circulation treatmentfluid 122 that does not contact a lost circulation zone 125 may then becirculated back to the surface, either with or without the presence ofanother fluid (e.g., drilling fluid) via an annulus 126 defined betweenthe drill string 108 and the walls of the wellbore 116. At the surface,the recirculated or spent lost circulation treatment fluid 122 exits theannulus 126 and may be conveyed to one or more fluid processing unit(s)128 via an interconnecting flow line 130. After passing through thefluid processing unit(s) 128, a “cleaned” lost circulation treatmentfluid 122 may be deposited into a nearby retention pit 132 (i.e., a mudpit). While illustrated as being arranged at the outlet of the wellbore116 via the annulus 126, those skilled in the art will readilyappreciate that the fluid processing unit(s) 128 may be arranged at anyother location in the drilling assembly 100 to facilitate its properfunction, without departing from the scope of the scope of thedisclosure.

In embodiments, the lost circulation treatment fluid 122, whichcomprises the set-delayed cement compositions disclosed herein, may beadded to a mixing hopper 134 communicably coupled to or otherwise influid communication with the retention pit 132. The mixing hopper 134may include, but is not limited to, mixers and related mixing equipmentknown to those skilled in the art. In alternative embodiments, however,the lost circulation treatment fluid 122 may not be added to a mixinghopper. In at least one embodiment, for example, there could be morethan one retention pit 132, such as multiple retention pits 132 inseries. Moreover, the retention put 132 may be representative of one ormore fluid storage facilities and/or units where the disclosedset-delayed cement compositions may be stored, reconditioned, and/orregulated until desired for use, e.g., as lost circulation treatmentfluid 122.

As mentioned above, the disclosed lost circulation treatment fluid 122which comprises the set-delayed cement compositions disclosed herein,may directly or indirectly affect the components and equipment of thedrilling assembly 100. For example, the disclosed lost circulationtreatment fluid 122 may directly or indirectly affect the fluidprocessing unit(s) 128 which may include, but is not limited to, one ormore of a shaker (e.g., shale shaker), a centrifuge, a hydrocyclone, aseparator (including magnetic and electrical separators), a desilter, adesander, a separator, a filter (e.g., diatomaceous earth filters), aheat exchanger, any fluid reclamation equipment. The fluid processingunit(s) 128 may further include one or more sensors, gauges, pumps,compressors, and the like used store, monitor, regulate, and/orrecondition the exemplary lost circulation treatment fluid 122.

The lost circulation treatment fluid 122 may directly or indirectlyaffect the pump 120, which representatively includes any conduits,pipelines, trucks, tubulars, and/or pipes used to fluidically convey thelost circulation treatment fluid 122 downhole, any pumps, compressors,or motors (e.g., topside or downhole) used to drive the lost circulationtreatment fluid 122 into motion, any valves or related joints used toregulate the pressure or flow rate of the lost circulation treatmentfluid 122, and any sensors (i.e., pressure, temperature, flow rate,etc.), gauges, and/or combinations thereof, and the like. The disclosedlost circulation treatment fluid 122 may also directly or indirectlyaffect the mixing hopper 134 and the retention pit 132 and theirassorted variations.

The disclosed lost circulation treatment fluid 122 may also directly orindirectly affect the various downhole equipment and tools that may comeinto contact with the lost circulation treatment fluid 122 such as, butnot limited to, the drill string 108, any floats, drill collars, mudmotors, downhole motors and/or pumps associated with the drill string108, and any MWD/LWD tools and related telemetry equipment, sensors ordistributed sensors associated with the drill string 108. The disclosedlost circulation treatment fluid 122 may also directly or indirectlyaffect any downhole heat exchangers, valves and corresponding actuationdevices, tool seals, packers and other wellbore isolation devices orcomponents, and the like associated with the wellbore 116. The disclosedset-delayed cement composition may also directly or indirectly affectthe drill bit 114, which may include, but is not limited to, roller conebits, PDC bits, natural diamond bits, any hole openers, reamers, coringbits, etc.

While not specifically illustrated herein, the disclosed lostcirculation treatment fluid 122 may also directly or indirectly affectany transport or delivery equipment used to convey the lost circulationtreatment fluid 122 to the drilling assembly 100 such as, for example,any transport vessels, conduits, pipelines, trucks, tubulars, and/orpipes used to fluidically move the lost circulation treatment fluid 122from one location to another, any pumps, compressors, or motors used todrive the lost circulation treatment fluid 122 into motion, any valvesor related joints used to regulate the pressure or flow rate of the lostcirculation treatment fluid 122, and any sensors (i.e., pressure andtemperature), gauges, and/or combinations thereof, and the like.

FIGS. 2 and 3 illustrate an example technique for placing a lostcirculation treatment fluid 214 comprising the set-delayed cementcompositions disclosed herein into a lost circulation zone 225 whilecementing equipment and casing are present in the wellbore 222. Such anembodiment may be used, for example, when it is desired to reduce theloss of displacement fluid into a lost circulation zone 225. FIG. 2illustrates surface equipment 210 that may be used in placement of lostcirculation treatment fluid 214 in accordance with certain embodiments.It should be noted that while FIG. 2 generally depicts a land-basedoperation, those skilled in the art will readily recognize that theprinciples described herein are equally applicable to subsea operationsthat employ floating or sea-based platforms and rigs, without departingfrom the scope of the disclosure. Additionally, it should be noted thatlost circulation treatment fluid 214 may be introduced prior to,concurrently with, or subsequent to the introduction of any othertreatment fluid (e.g., a displacement fluid, competition fluid, etc.)into wellbore 222. As illustrated by FIG. 2, the surface equipment 210may include a cementing unit 212, which may include one or more cementtrucks. The cementing unit 212 may include mixing equipment 204 andpumping equipment 206 as will be apparent to those of ordinary skill inthe art. The cementing unit 212 may pump lost circulation treatmentfluid 214 through a feed pipe 216 and to a cementing head 218 whichconveys the lost circulation treatment fluid 214 downhole.

Turning now to FIG. 3, the lost circulation treatment fluid 214,comprising the set-delayed cement compositions disclosed herein, may beplaced into a subterranean formation 220 in accordance with exampleembodiments. As illustrated, wellbore 222 may be drilled into thesubterranean formation 220. While wellbore 222 is shown extendinggenerally vertically into the subterranean formation 220, the principlesdescribed herein are also applicable to wellbores that extend at anangle through the subterranean formation 220, such as horizontal andslanted wellbores. As illustrated, the wellbore 222 comprises walls 224with lost circulation zones 225. In the illustrated embodiment, asurface casing 226 has been inserted into the wellbore 222. The surfacecasing 226 may be cemented to the walls 224 of the wellbore 222 bycement sheath 228. In the illustrated embodiment, one or more additionalconduits (e.g., intermediate casing, production casing, liners, etc.),shown here as casing 230 may also be disposed in the wellbore 222. Asillustrated, there is a wellbore annulus 232 formed between the casing230 and the walls 224 of the wellbore 222 and/or the surface casing 226.One or more centralizers 234 may be attached to the casing 230, forexample, to centralize the casing 230 in the wellbore 222 prior to andduring the cementing operation.

With continued reference to FIG. 3, the lost circulation treatment fluid214 may be pumped down the interior of the casing 230. The lostcirculation treatment fluid 214 may be allowed to flow down the interiorof the casing 230 through the casing shoe 242 at the bottom of thecasing 230 and up around the casing 230 into the wellbore annulus 232.As the lost circulation treatment fluid 214 flows upward through theannulus 232, lost circulation treatment fluid 214 may contact lostcirculation zones 225. If lost circulation treatment fluid 214 contactsa lost circulation zone 225, lost circulation treatment fluid 214 mayflow into lost circulation zone 225 and may become static ifsufficiently removed from a shear force. If static, lost circulationtreatment fluid 214 may rapidly develop gel strength. Once sufficientlygelled, lost circulation treatment fluid 214 may then seal lostcirculation zone 225 and prevent the loss of any treatment fluids (notshown) that subsequently flow adjacent to lost circulation zone 225.Over time, lost circulation treatment fluid 214 may be allowed to hardenand set in lost circulation zone 225, for example, to form a cementsheath that supports and positions the casing 230 in the wellbore 222.While not illustrated, other techniques may also be utilized forintroduction of the lost circulation treatment fluid 214. By way ofexample, reverse circulation techniques may be used that includeintroducing the lost circulation treatment fluid 214 into the lostcirculation zone 225 by way of the wellbore annulus 232 instead ofthrough the casing 230.

Any of the lost circulation treatment fluid 214 that does not contact alost circulation zone 225 may exit the wellbore annulus 232 via a flowline 238 and be deposited, for example, in one or more retention pits240 (e.g., a mud pit), as shown on FIG. 2.

As will be appreciated by those of ordinary skill in the art,embodiments of the set-delayed cement compositions may be used in avariety of cementing operations, including primary and remedialcementing. In some embodiments, a set-delayed cement composition may beprovided that comprises water, pumice, hydrated lime, a set retarder,and optionally a dispersant. The set-delayed cement composition may beintroduced into a subterranean formation and allowed to set therein. Asused herein, introducing the set-delayed cement composition into asubterranean formation includes introduction into any portion of thesubterranean formation, including, without limitation, into a wellboredrilled into the subterranean formation, into a near wellbore regionsurrounding the wellbore, or into both. Embodiments may further includeactivation of the set-delayed cement composition. The activation of theset-delayed cement composition may comprise, for example, addition of acement set activator to the set-delayed cement composition.

In primary cementing embodiments, for example, embodiments of theset-delayed cement composition may be introduced into a space between awall of a wellbore and a conduit (e.g., pipe strings, liners) located inthe wellbore, the wellbore penetrating the subterranean formation. Theset-delayed cement composition may be allowed to set to form an annularsheath of hardened cement in the space between the wellbore wall and theconduit. Among other things, the set cement composition may form abarrier, preventing the migration of fluids in the wellbore. The setcement composition also may, for example, support the conduit in thewellbore.

In remedial cementing embodiments, a set-delayed cement composition maybe used, for example, in squeeze-cementing operations or in theplacement of cement plugs. By way of example, the set-delayedcomposition may be placed in a wellbore to plug an opening, such as avoid or crack, in the formation, in a gravel pack, in the conduit, inthe cement sheath, and/or a microannulus between the cement sheath andthe conduit.

In embodiments, the set-delayed cement composition may be used fordifferent subterranean operations. In embodiments, the set-delayedcement composition may be used for one or more subterranean operationsat a specific worksite. As discussed above, the set-delayed cementcomposition may serve as a treatment fluid for these differentsubterranean operations. In embodiments, the set-delayed cementcomposition may be used as a lost circulation treatment fluid and whenset as a cementing composition that may support and position a casing ina wellbore. In embodiments, the set-delayed cement composition may bereused or recirculated in the wellbore for the same or a differentoperation. The reusability of the set-delayed cement composition allowsfor the recycling of the set-delayed cement composition. Furthermore,this process reduces the amount of equipment and manpower needed betweenoperations in regards to transitioning between operations, fluidhandling, and fluid storage.

The exemplary set-delayed cement composition disclosed herein maydirectly or indirectly affect one or more components or pieces ofequipment associated with the preparation, delivery, recapture,recycling, reuse, and/or disposal of the disclosed set-delayed cementcomposition. For example, the disclosed set-delayed cement compositionmay directly or indirectly affect one or more mixers, related mixingequipment, mud pits, storage facilities or units, compositionseparators, heat exchangers, sensors, gauges, pumps, compressors, andthe like used generate, store, monitor, regulate, and/or recondition theexemplary set-delayed cement composition. The disclosed set-delayedcement composition may also directly or indirectly affect any transportor delivery equipment used to convey the set-delayed cement compositionto a well site or downhole such as, for example, any transport vessels,conduits, pipelines, trucks, tubulars, and/or pipes used tocompositionally move the set-delayed cement composition from onelocation to another, any pumps, compressors, or motors (e.g., topside ordownhole) used to drive the set-delayed cement composition into motion,any valves or related joints used to regulate the pressure or flow rateof the set-delayed cement composition, and any sensors (i.e., pressureand temperature), gauges, and/or combinations thereof, and the like. Thedisclosed set-delayed cement composition may also directly or indirectlyaffect the various downhole equipment and tools that may come intocontact with the set-delayed cement composition such as, but not limitedto, wellbore casing, wellbore liner, completion string, insert strings,drill string, coiled tubing, slickline, wireline, drill pipe, drillcollars, mud motors, downhole motors and/or pumps, cement pumps,surface-mounted motors and/or pumps, centralizers, turbolizers,scratchers, floats (e.g., shoes, collars, valves, etc.), logging toolsand related telemetry equipment, actuators (e.g., electromechanicaldevices, hydromechanical devices, etc.), sliding sleeves, productionsleeves, plugs, screens, filters, flow control devices (e.g., inflowcontrol devices, autonomous inflow control devices, outflow controldevices, etc.), couplings (e.g., electro-hydraulic wet connect, dryconnect, inductive coupler, etc.), control lines (e.g., electrical,fiber optic, hydraulic, etc.), surveillance lines, drill bits andreamers, sensors or distributed sensors, downhole heat exchangers,valves and corresponding actuation devices, tool seals, packers, cementplugs, bridge plugs, and other wellbore isolation devices, orcomponents, and the like.

To facilitate a better understanding of the present embodiments, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the embodiments.

Example 1

A sample lost circulation treatment fluid comprising a set-delayedcement composition was prepared. The sample comprised pumice (DS-325lightweight aggregate), hydrated lime, Micro Matrix® cement retarder,and water. The compositional makeup of the sample is presented in Table1 below:

TABLE 1 Compositional Makeup of Lost Circulation Treatment Fluid Example1 Component Amount (kilograms) % bwoP* Pumice 48.5 100.0 Lime 9.7 20.0Retarder 0.61 1.25 Co-Retarder 0.24 0.50 Water 31.5 65.0 Dispersant 0.290.60 Weighting Agent 0.97 2.0 *bwoP = by weight of Pumice

The sample was aged at room temperature and rheology measurements weretaken by a Model 35A Fann Viscometer equipped with a Fann Yield StressAdapter (FYSA) and a No. 1 spring, in accordance with the procedure setforth in API RP Practice 10B-2, Recommended Practice for Testing WellCements. The measurements were used to calculate the shear-thinningindex (n) of the sample as it aged using the Herschel-Bulkley fluidmodel as discussed above. The results of this test are set forth inTable 2 below.

TABLE 2 Shear-Thinning Index of Lost Circulation Treatment Fluid Example1 Fluid Age Yield Stress Shear-Thinning (Days) (lb/100 ft²) Index 0 8.40.91 1 14.5 0.65 4 21.2 0.74 5 28.0 0.84 7 29.2 0.88 10* 2.1 0.78 12 10.1 0.80 *0.1% dispersant added by weight of Pumice

Additionally 3 separate samples were removed and additional testingparameters, either the addition of a cement set activator or an increasein temperature, were performed on each sample. The results of these testare set forth in Table 3 below.

TABLE 3 Shear-Thinning Index of Lost Circulation Treatment Fluid Example1 Fluid Age Yield Stress Shear-Thinning (Days) (lb/100 ft²) IndexTemperature Activator 7 4 0.74 — 10% CaCl₂ 8 35.8 0.61 140° F. — 8 14.70.59 180° F. —

The results indicate that the lost circulation treatment fluid sampleexhibits shear-thinning behavior over a span of 12 days. Furthermore,the sample remains shear-thinning even in the presence of a cement setactivator or at elevated temperatures.

The original sample was portioned into three portions and tested withthree different cement set activators to measure compressive strength.The three different cement set activators were sodiumhexametaphosphate-1 (SHMP-1), sodium hexametaphosphate-2 (SHMP-2), and a10% calcium chloride solution. The formulations for the SHMP activatorsare described in Table 4 below. The samples were then poured into 2″ by4″ plastic cylinders and cured for 24 hours at 140° F. in a water bath.After the samples were cured, the destructive compressive strength wasmeasured by using a mechanical press to crush the samples in accordancewith the procedure set forth in API RP Practice 10B-2, RecommendedPractice for Testing Well Cements. The results are presented in Table 5below.

TABLE 4 SHMP Cement Set Activator Formulations SHMP-1 SHMP-2 ComponentAmount % bw Amount % bw SHMP 62.7 g 5.50% 62.7 g 5.50% Sodium Sulfate62.7 g 5.50% 62.7 g 5.50% Dispersant   15 g 1.32%  7.5 g 0.66% Water   1kg 87.69%  1.0 kg 87.69%

TABLE 5 Compressive Strength Values (psi) of Lost Circulation TreatmentFluid Example 1 Activator % bwoP Avg. CS (psi) 2% SHMP-1 757.0 2% SHMP-2677.5 10% CaCl₂ 193.5

The results indicate that the lost circulation treatment fluid sampleexhibits good compressive strength values, particularly with the SHMPcement set activators and thus may serve the purpose of supporting awell structure in addition to stopping lost circulation.

Example 2

A sample lost circulation treatment fluid comprising a set-delayedcement composition was prepared. The sample comprised pumice (DS-325lightweight aggregate), hydrated lime, Micro Matrix® cement retarder,and water. The compositional makeup of the sample is presented in Table6 below:

TABLE 6 Compositional Makeup of Lost Circulation Treatment Fluid Example2 Component Amount (kilograms) % bwoP* Pumice 500.0 100.0 Lime 100.020.0 Retarder 6.25 1.25 Co-Retarder 2.50 0.50 Water 300.0 60.0Dispersant 3.0 0.60 Weighting Agent 10.0 2.0 *bwoP = by weight of Pumice

The sample was aged at room temperature and rheology measurements weretaken by a Model 35A Fann Viscometer equipped with a Fann Yield StressAdapter (FYSA) and a No. 1 spring, in accordance with the procedure setforth in API RP Practice 10B-2, Recommended Practice for Testing WellCements. The measurements were used to calculate the shear-thinningindex (n) of the sample as it aged using the Herschel-Bulkley fluidmodel as discussed above. The results of this test are set forth inTable 7 below.

TABLE 7 Shear-Thinning Index of Lost Circulation Treatment Fluid Example2 Fluid Age Yield Stress Shear-Thinning (Days) (lb/100 ft²) Index 2 17.60.51 7 22.4 0.98 14 17.2 0.80 21 7.8 0.73

Additionally 3 separate samples were removed and additional testingparameters, either the addition of a cement set activator and anincrease in temperature, were performed on each sample. The results ofthese tests are set forth in Table 8 below.

TABLE 8 Shear-Thinning Index of Lost Circulation Treatment Fluid Example2 Fluid Age Yield Stress Shear-Thinning (Days) (lb/100 ft²) IndexTemperature Activator 7 1.2 0.57 134° F. 10% CaCl₂ 7 4.8 0.19 134° F. 2%SHMP/ NaSO₄ 14 7.4 0.48 183° F. 10% CaCl₂

The results indicate that the lost circulation treatment fluid sampleexhibits shear-thinning behavior over a span of 21 days. Furthermore,the sample remains shear-thinning even in the presence of a cement setactivator and at elevated temperatures.

The sample was then aged over a 35 day period and introduced to either aCaCl₂ or SHMP/NaSO₄ cement set activator. Portions of the samples weretaken at regular time points and their compressive strength wasmeasured. The samples were then poured into 2″ by 4″ brass cylinders andcured for 24 hours at 134° F. in a water bath. After the samples werecured, the destructive compressive strength was measured by using amechanical press to crush the samples in accordance with the procedureset forth in API RP Practice 10B-2, Recommended Practice for TestingWell Cements. The results are presented in Table 9 below.

TABLE 9 Compressive Strength Values (psi) of Lost Circulation TreatmentFluid Example 2 Fluid Age (Days) 10%* CaCl₂ 2%* SHMP/NaSO₄ 0 <50 108 1<50 380 2 <50 552 7 — 485 14 30 705 21 35 513 28 358 899 35 22 440 *bwoP= by weight of Pumice

The results indicate that the lost circulation treatment fluid sampleexhibits good compressive strength values, particularly with theSHMP/NaSO₄ cement set activator and thus may serve the purpose ofsupporting a well structure in addition to stopping lost circulation.

Example 3

Two sample lost circulation treatment fluids comprising a set-delayedcement composition were prepared. The samples comprised pumice (DS-325lightweight aggregate), hydrated lime, Micro Matrix® cement retarder,and water. To the experimental sample, a 33% aluminum sulfate solutionwas added. The control sample did not comprise any aluminum sulfatesolution. The compositional makeup of the samples are presented in Table10 below:

TABLE 10 Compositional Makeup of Lost Circulation Treatment FluidExample 3 Component Amount (grams) % bwoP* Pumice 271.8 100.0 Lime 54.120.0 Retarder 3.24 1.25 Co-Retarder 0.68 0.25 Water 163.1 60.0Dispersant 1.55 0.60 Weighting Agent 5.4 2.0 Viscosifier 0.08 0.035 33%Aluminum Sulfate 6.3 2.3 *bwoP = by weight of Pumice, **Al₂(SO₄)₃ wasonly added to the experimental sample

The samples were aged at room temperature for 72 days. Rheologicalmeasurements were taken by a Model 35A Fann Viscometer equipped with aFann Yield Stress Adapter (FYSA) and a No. 1 spring, in accordance withthe procedure set forth in API RP Practice 10B-2, Recommended Practicefor Testing Well Cements. The results are presented in Table 11 below.

TABLE 11 Rheological Measurements RPM Sample 3 6 100 200 300 600 3D 6DControl 1 1 8 16.5 26 66 0.5 0 Experimental 30 31 44.5 54.5 66 105 20 18

The measurements were used to calculate the shear-thinning index (n) ofthe samples as they aged using the Herschel-Bulkley fluid model asdiscussed above. The results of this test are set forth in Table 12below.

TABLE 12 Shear-Thinning Index of Lost Circulation Treatment FluidExample 3 Fluid Age Yield Stress Shear-Thinning Sample (Days) (lb/100ft²) Index Experimental 72 0.8 0.19 Control 72 29 1.11

These results indicate that the aluminate solution greatly increases theduration that the fluid exhibits shear-thinning behavior.

It should be understood that the compositions and methods are describedin terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range are specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues even if not explicitly recited. Thus, every point or individualvalue may serve as its own lower or upper limit combined with any otherpoint or individual value or any other lower or upper limit, to recite arange not explicitly recited.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the invention covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present invention. Ifthere is any conflict in the usages of a word or term in thisspecification and one or more patent(s) or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. A lost circulation treatment fluid comprising:pumice, hydrated lime, a set retarder, and water.
 2. The lostcirculation treatment fluid of claim 1 wherein the lost circulationtreatment fluid has a shear-thinning index of less than 1 as calculatedby the Herschel-Bulkley model.
 3. The lost circulation treatment fluidof claim 1 wherein the lost circulation treatment fluid furthercomprises aluminum sulfate.
 4. The lost circulation treatment fluid ofclaim 1 wherein the set retarder comprises at least one retarderselected from the group consisting of a phosphonic acid, a phosphonicacid derivative, a lignosulfonate, a salt, an organic acid, acarboxymethylated hydroxyethylated cellulose, a synthetic co- orter-polymer comprising sulfonate and carboxylic acid groups, a boratecompound, and any mixture thereof.
 5. The lost circulation treatmentfluid of claim 1 wherein the lost circulation treatment fluid furthercomprises a dispersant selected from the group consisting of asulfonated-formaldehyde-based dispersant, a polycarboxylated etherdispersant, and any combination thereof.
 6. The lost circulationtreatment fluid of claim 1 wherein the set retarder comprises aphosphonic acid derivative, and wherein the set-delayed cementcomposition further comprises a polycarboxylated ether dispersant. 7.The lost circulation treatment fluid of claim 1 wherein the lostcirculation treatment fluid further comprises a cement set activator,and wherein the cement set activator comprises at least one cement setactivator selected from the group consisting of calcium chloride,triethanolamine, sodium silicate, zinc formate, calcium acetate, sodiumhydroxide, sodium sulfate, nanosilica, sodium hexametaphosphate, and anycombinations thereof.
 8. The lost circulation treatment fluid of claim 1wherein the lost circulation treatment fluid has a density in the rangeof from about 8 lb/gal to about 17 lb/gal.
 9. A lost circulationtreatment fluid comprising: pumice, hydrated lime, a set retarder, andwater; wherein the lost circulation treatment fluid has a shear-thinningindex of less than 1 as calculated by the Herschel-Bulkley model,wherein the lost circulation treatment fluid has a static gel strengthof at least about 100 lb/100 ft² at a temperature of about 50° F. toabout 200° F.
 10. The lost circulation treatment fluid of claim 9wherein the lost circulation treatment fluid has a shear-thinning indexof less than 1 as calculated by the Herschel-Bulkley model.
 11. The lostcirculation treatment fluid of claim 9 further comprising aluminumsulfate.
 12. The lost circulation treatment fluid of claim 9 wherein theset retarder comprises at least one retarder selected from the groupconsisting of a phosphonic acid, a phosphonic acid derivative, alignosulfonate, a salt, an organic acid, a carboxymethylatedhydroxyethylated cellulose, a synthetic co- or ter-polymer comprisingsulfonate and carboxylic acid groups, a borate compound, and any mixturethereof.
 13. The lost circulation treatment fluid of claim 9 furthercomprising a dispersant selected from the group consisting of asulfonated-formaldehyde-based dispersant, a polycarboxylated etherdispersant, and any combination thereof.
 14. The lost circulationtreatment fluid of claim 9 wherein the set retarder comprises aphosphonic acid derivative, and wherein the set-delayed cementcomposition further comprises a polycarboxylated ether dispersant. 15.The lost circulation treatment fluid of claim 9 further comprising acement set activator, and wherein the cement set activator comprises atleast one cement set activator selected from the group consisting ofcalcium chloride, triethanolamine, sodium silicate, zinc formate,calcium acetate, sodium hydroxide, sodium sulfate, nanosilica, sodiumhexametaphosphate, and any combinations thereof.
 16. The lostcirculation treatment fluid of claim 9 wherein the lost circulationtreatment fluid is a set-delayed cement composition capable of remainingin a pumpable fluid state for about 1 day or longer at a temperature ofabout 100° F.
 17. The lost circulation treatment fluid of claim 9wherein the lost circulation treatment fluid has a static gel strengthof at least about 500 lb/100 ft² at a temperature of about 50° F. toabout 200° F.
 18. A lost circulation treatment system comprising: a lostcirculation treatment fluid comprising: pumice, hydrated lime, a setretarder, and water, wherein the lost circulation treatment fluid is aset-delayed cement composition capable of remaining in a pumpable fluidstate for about 1 day or longer at a temperature of about 100° F.; and acement set activator.
 19. The lost circulation treatment system of claim18 wherein the lost circulation treatment fluid has a shear-thinningindex of less than 1 as calculated by the Herschel-Bulkley model. 20.The lost circulation treatment system of claim 18 wherein the lostcirculation treatment fluid has a static gel strength of at least about100 lb/100 ft² at a temperature of about 50° F. to about 200° F.